This invention relates to a paste of the type used to apply a layer of sinterable palladium particles that are subsequently sintered to form a palladium film on a ceramic substrate. More particularly, this invention relates to a palladium paste that includes additions of a titanium dioxide powder and a metal titanate powder to enhance adhesion of the film to the substrate. In one aspect, this invention relates to a co-firing process in which the paste is applied to a ceramic powder base, and the coated base is heated to sinter the ceramic powder to complete the substrate and to concurrently sinter the palladium powder to form a film bonded to the substrate.
In the manufacture of an electronic component or the like, it is known to utilize a co-firing process to form a metal film onto a ceramic substrate. The substrate is derived from a base of ceramic powder and an expendable organic binder. The metal film is formed from metal powder that is suspended in a liquid vehicle to form a paste that permits the powder to be applied by convenient techniques, such as spraying or screen printing. The paste is applied to the base and dried to form a particulate layer. An expendable organic binder may be included in the paste to improve bonding of the particles within the layer. The base and the applied layer are heated to a temperature and for a time sufficient to sinter the ceramic powder to form the substrate and concurrently to sinter the metal powder to form a film bonded to the substrate.
Substrates formed of a metal titanate compound, such as strontium calcium titanate (SCT), may require relatively high sintering temperatures greater than about 1,250.degree. C. Many metals have melting points less than this higher sintering temperature and are not suitable for forming co-fired films on titanate substrates. Palladium is sinterable at the higher temperature, but tends to form a film having poor adhesion to the underlying ceramic. Therefore, there is a need to improve adhesion of a palladium film formed from a paste applied to a ceramic substrate and, in particular, to a substrate that is concurrently formed in a co-firing process carried out at a relatively higher temperature.